I have had trouble reaching 2 Verizon cellphone users from my OOma. I get a busy signal (even though the person is not on their phone) - and it doesn't roll to voice mail (like it would if they were on their phone). They are in the same area code (651) as my phone . I have tried 7 and 10 digit dialing. Do I need to dial a 1 first ? Any other sugestions ?